As shown in FIG. 1, a multi joint robot 100 may comprise a first arm 101 and a second arm 102. An upper portion of the first arm 101 may be provided with two protrusions 105 and 106, which are substantially parallel to each other. A lower portion of the first arm may comprise a hollow supporting member 103, which may be used for carrying a device such as a motor or the like. The second arm 102 is rotatably connected to the two protrusions 105 and 106, so that the second arm 102 is supported by the two protrusions and is caused to rotate around an axis 0.
Usually the first arm may be cast using sand casting or pressure casting. Pressure casting is advantageous in dimension precision and stability and also has a low casting cost.
However, as shown in FIG. 2, regarding such a casting as the first arm 101 with an inward recess part 201, when the casting is completed, a casting mold 202 cannot be taken out. Moreover, in order to receive the robot's necessary components such as gears, synchronous belts and cables, the first arm 101 is usually designed into a hollow shape, and such a shape also prevents the mold 202 from being taken out when the casting is completed.
Due to the foregoing technical problems, sand casting is usually used in the prior art when making the robot's first arm 101. However, the first arm manufactured by sand casting is overweight and has a low dimension precision as well as high manufacturing expenses.
In order to use pressure casting, as shown in FIG. 7, the prior art further discloses that the first arm 101 is divided through a partitioning surface P1 into two half portions 701 and 702 which are die-cast separately, and then the two half portions are connected to obtain a complete first arm 101. However, in the prior art, the two half portions 701 and 702 are symmetrically shaped, and the supporting member at the bottom of the first arm is also divided into the two half portions. Thereby, when connecting the two half portions, the position needs to be adjusted in four directions, so that the precision of connection can hardly be guaranteed. In addition, dividing the supporting member may cause its mechanical performance to be affected.